1. Field of the Invention
The present invention relates to a numerical controller having a function of controlling an oscillating operation of a grinding tool on a grinding machine.
2. Description of the Related Art
A grinding machine that grinds a machine tool executes an oscillating operation for grinding a side face of a workpiece by moving a Z-axis in vertical direction as well as moving X-axis and Y-axis together with the movement of the Z-axis.
U.S. Patent Application Publication No. 2005/0215176 A1 describes a numerical controller that controls two or more control axes for performing a contouring control, the apparatus having chopping movement data generating means that simultaneously controls the two or more control axes so as to perform a chopping operation, and at the same time, generates movement data for performing the contouring control.
Japanese Patent Application Laid-Open No. 4-8473 describes that a numerical controller employing a chopping control system for controlling a chopping operation of a grinding tool includes chopping distance calculating means for calculating a chopping distance from designated a upper dead point and a lower dead point, a correction table that stores a chopping correction value corresponding to a chopping speed, and an adder that adds the chopping distance and the chopping correction value to calculate a chopping distance command value.
Japanese Patent Application Laid-Open No. 9-230920 describes that only a specific region is processed by changing a cut amount and a feed speed of a tool in the region set beforehand to an NC machine tool, in order to shorten a processing time in a cutting workpiece. Japanese Patent Application Laid-Open No. 11-65633 describes that a ratio of a feed speed to a revolution of a spindle is changed with respect to a set region. Japanese Patent Application Laid-Open No. 8-243799 describes a punch operation control apparatus that subdivides a path of a punch tool, and treats even the same position as a different position, whereby a speed can be changed for every section in a punch press machine.
The speed control in the oscillating operation described in the above-mentioned U.S. Patent Application Publication No. 2005/0215176 A1 and Japanese Patent Application Laid-Open No. 4-8473 outputs a moving amount with a designated constant speed. Therefore, an acceleration/deceleration process is needed at a turn-around of a boundary point. Accordingly, an accumulation in the moving amount is caused, which affects the precision of the boundary point.
Japanese Patent Application Laid-Open No. 4-8473 described above discloses a technique of correcting the accumulation in the moving amount due to the acceleration/deceleration process and a delay of a servo motor. Depending upon the designation of a speed and a time constant during the acceleration and deceleration, the accumulation in the moving amount during the acceleration and deceleration increases, and hence, the correction amount increases. Accordingly, it takes much time to complete the correction.
In the technique described in Japanese Patent Application Laid-Open No. 9-230920 and Japanese Patent Application Laid-Open No. 11-65633, the designated region is treated with a bit pattern. Therefore, the determination as to the difference in the moving direction is not made. In the oscillating operation, even the same position is needed to be treated as a different position, when the moving direction is different. Therefore, prior art described in Japanese Patent Application Laid-Open No. 9-230920 and Japanese Patent Application Laid-Open No. 11-65633 cannot be applied to the oscillating operation.
In the technique described in Japanese Patent Application Laid-Open No. 8-243799, the position of each section is changed depending upon a thickness of a workpiece. However, this technique originally aims a control of a punch operation, and a continuous control such as the oscillating operation is not supposed. Further, this technique does not assume the change in the path, so that it cannot be applied to the case where the oscillating region is shifted.